N6 -tricyclic adenosines for treating hypertension

ABSTRACT

N6-Tricyclic adenosines and pharmaceutically acceptable acid addition salts having highly desirable central nervous system and cardiovascular properties, processes for their manufacture and pharmaceutical composition and methods for using said compounds and compositions are described.

This is a division of application Ser. No. 665,219 filed Oct. 4, 1984; now U.S. Pat. No. 4,593,019.

BACKGROUND OF THE INVENTION

The compounds of the instant invention are adenosine analogs having some of the same activity as adenosine, but having a significantly longer duration of action. A distinguishing feature of these compounds from other adenosine analogs previously described, is the discovery that N⁶ -tricyclicalkyl adenosines have favourable ratio of affinities at A1 and A2 receptors and highly desirable central nervous system and cardiovascular activities, such as antipsychotic, sedative, or antihypertensive.

SUMMARY OF THE INVENTION

Accordingly, the present invention relates to a compound of the formula: ##STR1## wherein R^(6a) is hydrogen or lower alkyl; R^(6b) is hydrogen, hydroxy, lower alkyl, lower alkanoyloxy, or benzoyloxy; R^(6c) and R^(6d) are each independently hydrogen or one or more of the substituents halogen, hydroxy, lower alkoxy, lower alkanoyloxy, benzoyloxy, lower S(O)_(n) --alkyl in which n is 0, 1, or 2, sulfonamide, trifluoromethyl, lower alkyl, amino, lower mono- or dialkylamino, nitro, or sulfhydryl; X is a valence bond or a straight or branched alkylene of 1 to 8 carbon atoms; Y is a valence bond, oxygen, sulfur, NR in which R is hydrogen, lower alkyl, or lower alkanoyl or benzoyl, (CH₂)_(n) wherein n is 1 or 2, or CH═CH; R² is hydrogen, halogen, NR^(i) R^(ii), OR^(i), or SR^(i), in which R^(i) and R^(ii) are each independently hydrogen, lower alkyl, or phenyl lower alkyl; R^(2'), R^(3'), and R^(5') are each independently hydrogen or lower alkanoyl, benzoyl, or benzoyl substituted by lower alkyl, lower alkoxy, halogen, or trifluoromethyl; R^(2') and R^(3') may also be bonded together to form a lower alkylidene such as isopropylidene.

The present invention includes pharmaceutically acceptable salts, and where optical centers are present both the (R, S) and the separate (R) and (S) configurations; preferred sugar stereochemistry is that equivalent to a β-D-ribose.

The present invention also relates to a pharmaceutical composition comprising a therappeutically effective amount of a compound of the above formula I with a pharmaceutically acceptable carrier, and to a method of treating mammals by administering to such mammals a dosage form of a compound of the formula I as defined above.

DETAILED DESCRIPTION

In the compounds of the formula I, the term "lower alkyl" is meant to include a straight or branched alkyl group having from 1 to 6 carbon atoms such as, for example, methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, tert-butyl, amyl, isoamyl, neopentyl, hexyl, and the like.

Halogen includes particularly fluorine, chlorine or bromine.

Lower alkoxy and thioalkoxy are O-alkyl or S-alkyl of from 1 to 6 carbon atoms as defined above for "lower alkyl".

Lower alkanoyl is a straight or branched ##STR2## and lower alkanoyloxy is a straight or branched ##STR3## group of from 1 to 6 carbon atoms in the alkyl chain as defined above.

Lower mono- or dialkylamino is a straight or branched --NH alkyl or --N(alkyl)₂ group of from 1 to 6 carbon atoms in the alkyl chain defined above.

The compounds of formula I are useful both in the free base form and in the form of acid addition salts. Both forms are within the scope of the invention. In practice, use of the salt form amounts to use of the base form. Appropriate pharmaceutically acceptable salts within the scope of the invention are those derived from mineral acids such as hydrochloric acid and sulfuric acid; and organic acids such as ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and the like, giving the hydrochloride, sulfamate, ethanesulfonate, benzenesulfonate, p-toluenesulfonate, and the like, respectively.

The acid addition salts of said basic compounds are prepared either by dissolving the free base in aqueous or aqueous alcohol solution or other suitable solvents containing the appropriate acid and isolating the salt by evaporating the solution, or by reacting the free base and acid in an organic solvent, in which case the salt separates directly or can be obtained by concentration of the solution.

The compounds of the invention may contain asymmetric carbon atoms. The invention includes the individual enantiomers or diastereomers, and mixtures thereof. The individual enantiomers or diastereomers may be prepared or isolated by methods known in the art.

A preferred embodiment of the present invention is a compound of the formula I wherein R₆ ^(a) and R₆ ^(b) are hydrogen and R₆ ^(c), R₆ ^(d), R₂, X, Y, R₂ ', R₃ ', and R₅ ' are as defined above.

Another preferred embodiment of the present invention is a compound of formula I where R₆ ^(a), R₆ ^(b), R₆ ^(c), R₆ ^(d) are hydrogen and X, Y, R₂, R₂ ', R₃ ', and R₅ ' are as defined above.

Still another preferred embodiment of this invention is a compound of formula I wherein R₆ ^(a), R₆ ^(b), R₆ ^(c), R₆ ^(d) are hydrogen, X is a valence bond, methylene or ethylene, Y is a valence bond or oxygen and R₂, R₂ ', R₃ ', R₅ ' are as defined above.

Another preferred embodiment is a compound of the formula I where R₆ ^(a), R₆ ^(b), R₆ ^(c), and R₆ ^(d) are hydrogen, X is a valence bond, methylene or ethylene, Y is a valence bond or oxygen, R₂ is hydrogen and R₂ ', R₃ ', R₅ ' are as defined above.

A further preferred embodiment is a compound of the formula I wherein R₆ ^(a), R₆ ^(b), R₆ ^(c), and R₆ ^(d) are hydrogen, X is a valence bond, methylene or ethylene, Y is a valence bond or oxygen, and R₂, R₂ ', R₃ ', R₅ ' are hydrogen.

A particular embodiment includes N⁶ -fluorenyladenosine; N⁶ -fluorenymethyladenosine; N⁶ fluorenylethyladenosine, and N⁶ -(xanthene-9-methylamino)adenosine.

The compounds of formula I may be conveniently synthesized by reacting a 6-halopurine riboside of formula II with the requisite tricyclic or tricyclic alkyl amine of formula III in an inert solvent such as alcohol, or an aprotic solvent such as dimethylformamide between about 25° to about 130° C. for from 1-48 hours.

It is useful to add a base such as triethylamine, or calcium carbonate to neutralize the hydrogen halide formed as a byproduct of the reaction, but this can also be accomplished by using an extra equivalent of the tricyclic amine. It is also convenient, although not necessary, to protect the ribofuranose hydroxyl groups as acetate or benzoate esters which can be removed with ammonium hydroxide or sodium methoxide following the synthesis of the N⁶ -substituted adenosine. The reaction is illustrated as follows: ##STR4## wherein Hal is halogen, preferably chlorine or bromine, and Y, R₂, R₆ ^(a), R₆ ^(b), R₆ ^(c), R₆ ^(d), R₂ ', R₃ ', and R₅ ' are as defined for formula I.

In addition, compounds of formula I wherein R₂ is other than hydrogen or halogen, may also be prepared from 2,6-dichloropurine riboside triacetate of formula IV in a stepwise manner, by first reacting a compound of the formula IV with the requisite tricyclic alkyl amine of formula III to give a compound of formula V, followed by replacing the chlorine atom at C₂ with the group R² using nucleophilic displacement conditions, and removing the acetate protecting groups as illustrated below. ##STR5##

The compounds of formula I have been found to possess differing affinities for adenosine receptors (designated A₁ and A₂ receptors for convenience). These compounds are active in animal tests which are predictive of neuroleptic activity for the treatment of major psychoses such as schizophrenia. The compounds of the invention also have sedative/hypnotic properties and as such, are useful for the treatment of sleep disorders. These compounds also have analgesic properties and as such, are useful in the treatment of pain.

In addition, the compounds of the present invention are useful as antihypertensive agents for the treatment of high blood pressure.

PHARMACOLOGICAL EVALUATION Adenosine Receptor Binding--A₁ Receptor Affinity (RBA1)

Preparation of Membranes

Whole brain minus cerebellum and brainstem from male Long Evans rats (150-200 g) was homogenized in 30 volumes of ice-cold 0.05M Tris-HCl buffer pH 7.7 using a Brinkman Polytron PT-10, (setting number 6 for 20 seconds) and centrifuged for ten minutes at 20,000×g (Sorvall RC-2), 4° C. The supernatant was discarded, and the pellet was resuspended and centrifuged as before. The pellet was resuspended in 20 ml Tris-HCl buffer containing two International Units/ml of adenosine deaminase (Sigma type III from calf intestinal mucosa), incubated at 37° C. for 30 minutes, then subsequently at 0° C. for ten minutes. The homogenate was again centrifuged, and the final pellet was resuspended in ice-cold 0.05M Tris-HCl buffer pH 7.7 to a concentration of 20 mg/ml original wet tissue weight and used immediately.

Assay Conditions

Tissue homogenate (10 mg/ml) was incubated in 0.05M Tris-HCl buffer pH 7.7 containing 1.0 nM [³ H]-N⁶ -cyclohexyladenosine [³ H]-CHA) with or without test agents in triplicate for one hour at 25° C. Incubation volume was 2 ml. Unbound [³ H]-CHA was separated by rapid filtration under reduced pressure through Whatman glass fiber (GF/B) filters. The filters were rinsed three times with 5 ml of ice cold 0.05M Tris-HCl buffer pH 7.7. The radio-labeled ligand retained on the filter was measured by liquid scintillation spectrophotometry after shaking the filters for one hour or longer on a mechanical shaker in 10 ml of Beckman Ready-Solv HP scintillation cocktail.

Calculations

Nonspecific binding was defined as the binding which occurred in the presence of 1 mM theophylline. The concentration of test agent which inhibited 50% of the specific binding (IC₅₀) was determined by nonlinear computer curve fit. The Scatchard plot was calculated by linear regression of the line obtained by plotting the amount of radioligand bound (pmoles/gram of tissue) versus ##EQU1## Since the amount of radioligand bound was a small fraction of the total amount added, free radioligand was defined as the concentration (nM) of radioligand added to the incubation mixture. The Hill coefficient was calculated by linear regression of the line obtained by plotting the log of the bound radioligand vs the log of the ##EQU2## The maximal number of binding sites (B_(max)) was calculated from the Scatchard plot.

Adenosine Receptor Binding--A₂ Receptor Affinity (RBA2)

Tissue Preparation

Brains from 200-500 g mixed sex Sprague-Dawley rats were purchased from Pel-Freez (Rogers, Ark.). Fresh brains from male Long-Evans hooded rats (Blue Spruce Farms, Altamont, NY) gave essentially identical results. Brains were thawed and then kept on ice while the striata were dissected out. Striata were disrupted in 10 vol of ice-cold 50 mM Tris.HCl (pH 7.7 at 25° C., pH 8.26 at 5° C.) (Tris) for 30 seconds in a Polytron PT-10 (Brinkmann) at setting 5. The suspension was centrifuged at 50,000×g for ten minutes, the supernatant discarded, the pellet resuspended in 10 vol ice-cold Tris as above, recentrifuged, resuspended at 1 g/5 ml, and stored in plastic vials at -70° C. (stable for at least six months). When needed, tissue was thawed at room temperature, disrupted in a Polytron, and kept on ice until used.

Incubation Conditions

All incubations were for 60 minutes at 25° C. in 12×75 mm glass tubes containing 1 ml Tris with 5 mg original tissue weight of rat weight of rat striatal membranes, 4 nM [³ H]-N-ethyl adenosine-5'-carboxamide ([³ H]NECA), 50 nM N⁶ -cyclopentyladenosine (to eliminate A₁ receptor binding), 10 mM MgCl₂, 0.1 units/ml of adenosine deaminase and 1% dimethylsulfoxide. N⁶ - Cyclopentyladenosine was dissolved at 10 mM in 0.02 N HCl and diluted in Tris. Stock solutions and dilutions of N⁶ -cyclopentyladenosine could be stored at -20° C. for several months. Test compounds were dissolved at 10 mM in dimethylsulfoxide on the same day as the experiment, and diluted in dimethylsulfoxide to 100× the final incubation concentration. Control incubations received an equal volume (10 μl) of dimethylsulfoxide; the resulting concentration of dimethylsulfoxide had no effect on binding. [³ H]NECA was diluted to 40 nM in Tris. The membrane suspension (5 mg/0.79 ml) contained sufficient MgCl₂ and adenosine deaminase to give 10 mM and 0.1 units/ml, respectively, finalc concentration in the incubation. For test compounds with IC₅₀ values less than 1 μM, the order of additions was test compound (10 μl), N⁶ -cyclopentyladenosine (100 μl), [³ H]NECA (100 μl), and membranes (0.79 ml). For test compounds with IC₅₀ values greater than 1 μM and limited water solubility, the order of additions (same volumes) was test compound, membranes, N⁶ -cyclopentyladenosine, and [³ H]NECA. After all additions, the rack of tubes was vortexed, and the tubes were then incubated for 60 min at 25° C. in a shaking water bath. The rack of tubes was vortexed an additional time halfway through the incubation.

Incubations were terminated by filtration through 2.4 cm GF/B filters under reduced pressure. Each tube was filtered as follows: the contents of the tube were poured onto the filter, 4 ml of ice-cold Tris were added to the tube and the contents poured onto the filter, and the filter was washed twice with 4 ml of ice-cold Tris. The filtration was complete in about twelve seconds. Filters were put in scintillation vials, 8 ml of Formula 947 scintillation fluid added, and the vials left overnight, shaken, and counted in a liquid scintillation counter at 40% efficiency.

Data Analysis

Nonspecific binding was defined as binding in the presence of 100 μM N⁶ -cyclopentyladenosine, and specific binding was was defined as total binding minus nonspecific binding. The IC₅₀ was calculated by weighted nonlinear least squares curve-fitting to the mass-action equation. ##EQU3## where Y is cpm bound

T is cpm total binding without drug

S is cpm specific binding without drug

D is the concentration of drug

and

K is the IC₅₀ of the drug

Weighting factors were calculated under the assumption that the standard deviation was proportional to the predicted value of Y. Nonspecific binding was treated as a very large (infinite) concentration of drug in the computer analysis.

The IC₅₀ values (nM) for adenosine A₁ and A₂ receptor affinity are reported in the table.

    ______________________________________                                         Receptor Binding                                                               Example      RBA-1 (nM) RBA-2 (nM)                                             ______________________________________                                         1            8600       51000                                                  2            5.6        6.9                                                    3            435        --                                                     4            85         65                                                     ______________________________________                                    

ANTIPSYCHOTIC EVALUATION

The compounds of the invention are new chemical substances which are useful as pharmaceutical agents for the treatment of psychoses. The antipsychotic activity of representative compounds of the invention was established by the Mouse Activity and Screen Test Procedure (MAST) described below.

Animals

Nine unfasted Swiss-Webster male mice weighing 20-30 g are equally divided into three groups for each drug dose to be tested. That is, data for each dose level was generated by three separate groups of three mice each.

Drugs

A minimum of three dose levels (10, 30, and 100 mg/kg) are tested for each drug. Treatments are administered intraperitoneally one hour prior to testing. All dosages are calculated as parent compound and given in volumes of 10 ml/kg. Compounds are dissolved or suspended in 0.2% Methocel. Control animals are injected with Methocel.

Testing:

A two part testing procedure is started one hour postinjection. First, the screen test (ST) is performed (see Pharmac. Biochem. Behav. 6, 351-353, 1977). Briefly this test consists of placing mice on individual wire screens which are then rotated 180 degrees at the start of a 60 second observation period. The number of mice falling off the inverted screen is recorded.

Immediately following the screeen test, the final phase of testing is initiated by placing each group of three mice in one actophotometer (Life Sciences, 22, 1067-1076, 1978). The actophotometer consists of a cylindrical chamber whose center is occupied by another cylinder which contains the illumination for six photocells located on the perimeter of the chamber. Six light-beam interruptions equal one count. Locomotor activity is recorded by computer at ten minute intervals for 60 minutes.

Data:

The data obtained from the screen test are expressed as percent of mice falling off the screen. Data derived from locomotor activity of drug treated mice are compared to the activity of vehicle treated animals and are expressed as percent inhibition of spontaneous locomotion. All percentages reported for inhibition of locomotion (LI) are based upon data accumulated for one hour. Both phases of testing are graded: A=60-100%; C=31-59%; and N=0-30%. An overall dose rating is obtained by the following criteria:

    ______________________________________                                         Inhibition of         Screen Test  Dose                                        Locomotion Rating                                                                           with     Failure Rating =                                                                            Rating                                      ______________________________________                                         A            --       N or C =     A                                           A            --       A =          C                                           C            --       N or C =     C                                           All other combinations =   N                                                   ______________________________________                                    

LAD refers to the lowest dose at which an A rating is achieved. Compounds which exhibit an overall dose rating of A at a dose of 100 milligrams/kilogram or less are considered active. Utilizing this procedure, an overall dose rating of A was obtained for the noted compound at the indicated dose. The compounds are identified in the Examples.

Antipsychotic Evaluation

    ______________________________________                                                              Inhibition of Screen                                                           Mouse Locomotion                                                                             Test                                        Example Dose mg/kg   Activity      Failure                                     ______________________________________                                         1       10           41             0                                                  30           60             0                                                  100          68             0                                          2        1           56            11                                                   3           94            33                                                  10           97            44                                                  30           97            55                                                  100          91            55                                          4        1           -5             0                                                   3           17             0                                                  10           72             0                                                  30           91            11                                                  100          91            44                                          ______________________________________                                    

Representative compounds of the invention (identified in the Examples) were also tested for antipsychotic activity according to the following protocol (SIDR). The noted compound has the indicated ED₅₀ values (mg/kg) and is considered active as an antipsychotic agent in the test procedure.

Procedure

Mature male Long-Evans rats or squirrel-monkeys are conditioned to push a lever in order to avoid a painful electric footshock. If the animal fails to push the lever, he receives a shock every ten seconds until the lever is pushed. Shocks can be terminated by pushing the lever. Thereafter, as long as the lever is pushed at least once every 20 seconds, there will be no shock.

Each animal acts as its own control; one weekly session is used to establish baseline behavior and another session later in the week is used as a drug session. Once patterns of avoidance are established, the effects of standard and unknown compounds are studied.

RESPONSE EVALUATION

All events are electronically programmed and the response to these events counted or used as feed-back to the program.

ANTIHYPERTENSIVE EVALUATION (AHP3)

The usefulness of the compounds of the present invention as antihypertensive agents is demonstrated by their effectiveness in standard pharmacological test procedures, for example, in causing a significant decrease in mean arterial blood pressure in the conscious rat. This test procedure is described in the following paragraphs.

A Method for the Direct Monitoring of Aortic Blood Pressure and Heart Rate from Conscious Rats

The continuous monitoring of pulsatile blood pressure (BP) from unrestrained conscious rats surgically equipped with polyethylene cannulas was accomplished by means of a computer assisted data capture scheme (CADCS). The basic elements of the methodology are the cannulation procedure and the CADCS.

Method

Cannulation Procedure:

Rats were anesthetized with Telazol (1:1 tiletamine HCl and zolazepam HCl); 20-40 mg/kg IM and the descending aorta exposed via a midline incision. Cannulas fabricated from polyethylene tubing were inserted into the aorta via an undersized puncture hole below the renal arteries. The puncture hole was made by a 23 G disposable needle with a section of the aorta clamped off above and below the puncture site. The cannulas, consisting of a PE100 (0.86 mm ID) body and a PE50 (0.58 mm ID) tip, were attached to a trocar, inserted through the psoas muscle, and passed subcutaneously along the midline of the back and externalized between the ears. The cannulas were anchored to the psoas muscle and between the scalulae (3-0 green braided suture). The midline incision was closed in two steps (muscle first, skin second) using continuous over-and over sutures (4-0 chronic). Each rat was then given penicillin 30,000 units subcutaneously (Pencillin G Procaine Sterile Suspension).

The rats were fitted with a harness-spring-swivel assembly designed to protect the cannula and to provide the rat relative freedom of movement. The harnesses were fabricated from nylon hook and loop tape cemented to a metal plate to which spring wires (18-8 stainless steel), were attached to brass swivels. Each polyethylene cannula was channeled through a spring and connected through a swivel to a pressure transducer (Model P23Gb; Statham Instruments; Hato Rey, Puerto Rico) and an infusion pump (Sage model 234-7; Orion Research, Cambridge, MA) by means of PE100 tubing. While on test, each rat received a continuous slow infusion of heparinized saline solution (approximately 400 l or 40 units of heparin per 24 hour period) to prevent clot formation. Additional "flushes" of the cannula with heparinized saline were carried out when the aortic pulse pressure (systolic minus diastolic) was less than 25 mm Hg.

CADCS:

The pulsatile blood pressure and heart rate of each of 32 rats was monitored every minute by means of two in-laboratory microcomputers communicating directly with a data concentrator computer. The data were first stored on the data concentrator disk and then transferred to a magnetic tape for analysis and report generation by the main research computer. The overall scheme involved modulating the primary signal from the pressure transducer, generating the primary data set of the one-minute values for systolic, diastolic, and mean blood pressures and heart rate by the in-lab microcomputer and the storage, analysis, and report generation by the main reserach computer.

The transducers were connected to analog signal conditioning modules. The modules provided a regulated excitation voltage for the transducers, amplification as required to interface the microprocessors and an active low pass filter to compensate for the pressure wave form distortion produced by the flexible, fluid filled, narrow cannula. The distortion was 22-26 Hz and this provided a reliable estimate of both systolic and diastolic blood pressure.

The microcomputers (one for each of two groups of 16 rats) were connected to the input components through the module interface units, an analog-to-digital converter for the pressure wave form signal and the digital inputs for the dose and event marker switches. The microcomputer controlled the sequential acquisition of data from the modular interface units through an internal synchronous time-of-day clock/time base generator. Utilizing the time base generator as a reference, the blood pressure values and the marker switch status for each of the 32 stations were sampled every ten msec. The microcomputer processed each blood pressure sample as it was received to produce "running average" values for heart rate, and mean, systolic and diastolic blood pressures.

When tested by the above procedure, compounds of Examples produced the following changes in MAP and heart rate.

    ______________________________________                                                 At a Dose of 10 mg/kg                                                          Time (Hours)                                                                               MAP ↓                                                                            HR ↑                                        ______________________________________                                         Example 2 1             32%      24%                                                     3             32%      27%                                                     5             34%      20%                                                     7             28%      13%                                                     9             30%      13%                                           Example 4 1             11%      16%                                                     3              4%      19%                                                     5              8%      25%                                                     7             12%      15%                                                     9              8%      18%                                           ______________________________________                                    

ANALGESIC EVALUATION

The antiwrithing (AW) test provides preliminary assessment of compounds with potential analgesic activity. The test is performed in male Swiss-Webster mice. Compounds are administered subcutaneously in aqueous 0.2% methylcellulose or other appropriate vehicles in volumes of 10 ml/kg. Dosages represent active moiety.

Acetic acid (0.6%, 10 ml/kg) is injected intraperitoneally 20 minutes after administration of the adenosine agonist. Writhing movements are counted for five minutes starting seven minutes after the acetic acid injection. Writhing is defined as abdominal constriction and stretching of the body and hind legs with concave arching of the back. Data are expressed as ED₅₀ values, where the ED₅₀ is the dose necessary to suppress writhing by 50% relative to vehicle controls. ED₅₀ values are calculated by nonlinear regression analysis.

The biological data are summarized in the Table. Accordingly, the present invention also includes a pharmaceutical composition for treating psychoses, sleep disorders, pain, or hypertension comprising a corresponding antipsychotic, sedative, analgesic, or antihypertensive effective amount of a compound of the formula I as defined above together with a pharmaceutically acceptable carrier.

The present invention further includes a method for treating psychoses, sleep disorders, pain, or hypertension in mammals suffering therefrom comprising administering to such mammals either orally or parenterally a corresponding pharmaceutical composition containing a compound of the formula I as defined above in appropriate unit dosage form.

For preparing pharmaceutical compositions from the compounds described by this invention, inert, pharmaceutically acceptable carriers can be either solid or liquid. Solid form preparations include powders, tablets, dispersible granules, capsules, cachets, and suppositories. A solid carrier can be one or more substances which may also act as diluents, flavoring agents, solublizers, lubricants, suspending agents, binders or tablet disintegrating agents; it can also be encapsulating material. In powders, the carrier is a finely divided solid which is in admixture with the finely divided active compound. In the tablet the active compound is mixed with carrier having the necessary binding properties in suitable proportions and compacted in the shape and size desired. The powders and tablets preferably contain from 5 to 10 to about 70 percent of the active ingredient. Suitable solid carriers are magnesium carbonate, magnesium stearate, talc, sugar, lactose, pectin, dextrin, starch, gelatin, tragacanth, methylcellulose, sodium carboxymethylcellulose, a low melting wax, cocoa butter, and the like. The term "preparation" is intended to include the formulation of the active compound with encapsulating material as carrier providing a capsule in which the active component (with or without other carriers) is surrounded by carrier, which is thus in association with it. Similarly, cachets are included. Tablets, powders, cachets, and capsules can be used as solid dosage forms suitable for oral administration.

For preparing suppositories, a low melting wax such as a mixture of fatty acid glycerides or cocoa butter is first melted, and the active ingredient is dispersed homogeneously therein as by stirring. The molten homogeneous mixture is then poured into convenient sized molds, allowed to cool and thereby to solidify.

Liquid form preparations include solutions, suspensions, and emulsions. As an example may be mentioned water or water propylene glycol solutions for parenteral injection. Liquid preparations can also be formulated in solution in aqueous polyethylene glycol solution. Aqueous solutions suitable for oral use can be prepared by dissolving the active component in water and adding suitable colorants, flavors, stabilizing and thickening agents as desired. Aqueous suspensions suitable for oral use can be made by dispersing the finely divided active component in water with viscous material, i.e., natural or synthetic gums, resins, methylcellulose, sodium carboxymethylcellulose, and other well-known suspending agents.

Also included are solid form preparations which are intended to be converted, shortly before use, to liquid form preparations for either oral or parenteral administration. Such liquid forms include solutions, suspensions, and emulsions. These particular solid form preparations are most conveniently provided in unit dose form and as such are used to provide a single liquid dosage unit. Alternately, sufficient solid may be provided so that after conversion to liquid form, multiple individual liquid doses may be obtained by measuring predetermined volumes of the liquid form preparation as with a syringe, teaspoon, or other volumetric container. When multiple liquid doses are so prepared, it is preferred to maintain the unused portion of said liquid doses at low temperture (i.e., under refrigeration) in order to retard possible decomposition. The solid form preparations intended to be converted to liquid form may contain, in addition to the active material, flavorants, colorants, stabilizers, buffers, artificial and natural sweeteners, dispersants, thickeners, solubilizing agents, and the like. The liquid utilized for preparing the liquid form preparation may be water, isotonic water, ethanol, glycerine, propylene glycol, and the like as well as mixtures thereof. Naturally, the liquid utilized will be chosen with regard to the route of administration, for example, liquid preparations containing large amounts of ethanol are not suitable for parenteral use.

Preferably, the pharmaceutical preparation is in unit dosage form. In such form, the preparation is subdivided into unit doses containing appropriate quantities of the active component. The unit dosage form can be a packaged preparation, the package containing discrete quantities of preparation, for example, packeted tablets, capsules, and powders in vials or ampoules. The unit dosage form can also be a capsule, cachet, or tablet itself or it can be the appropriate number of any of these in packaged form.

The quantity of active compound in a unit dose of preparation may be varied or adjusted from 1 mg to 500 mg preferably to 5 to 100 mg according to the particular application and the potency of the active ingredient. The compositions can, if desired, also contain other compatible therapeutic agents.

In therapeutic use as described above, the mammalian dosage range for a 70 kg subject is from 0.1 to 150 mg/kg of body weight per day or preferably 1 to 50 mg/kg of body weight per day. The dosages, however, may be varied depending upon the requirements of the patient, the severity of the condition being treated, and the compound being employed. Determination of the proper dosage for a particular situation is within the skill of the art. Generally, treatment is initiated with smaller dosages which are less than the optimum dose of the compound. Thereafter the dosage is increased by small increments until the optimum effect under the circumstances is reached. For convenience, the total daily dosage may be divided and administered in portions during the day if desired.

The following Examples further illustrate the invention.

EXAMPLE 1

N⁶ -Fluorenyladenosine

4.0 g of 6-chloropurine riboside, 3.79 g of 9-aminofluorene hydrochloride and 3.52 g of triethylamine are refluxed in 100 ml ethanol under nitrogen for 20 hrs. the solvent is evaporated to dryness and residue is treated with 100 ml of cold water. Precipitated solid is filtered and treated with 50 ml of methanol-chloroform (1:1) affording 3.8 g (63%) of N⁶ -fluorenyladenosine having a m.p of 210°-212° C.

Anals. Calcd. for C₂₃ H₂₁ N₅ O₄.10H₂ O0.3HCl: C=60.00; H=5.09; N=15.21. Found: C=59.95; H=4.72; N=15.13.

EXAMPLE 2

N⁶ -Fluorenylmethyl adenosine

A mixture of 2.97 g of 6-chloropurine riboside, 2.25 g of fluorenylmethyl amine and 1.31 g of triethylamine is refluxed in 70 ml of ethanol under nitroen for 20 hrs. Upon cooling, solid material crystallizes out which is filtered and retreated with boiling ethanol. Solid material obtained is filtered and dried affording 2.9 g (63%) of N⁶ -fluorenylmethyl adenosine having a melting point of 139°-142° C.

Anals. Calcd. for C₂₄ H₂₃ N₅ O₄.0.25EtOH0.25H₂ O: C=63.75; H=5.45; N=15.17. Found: C=63.70; H=5.12; N=15.57.

EXAMPLE 3

N⁶ -Fluorenylethyl adenosine

A reaction mixture of 1.75 g of 6-chloropurine riboside, 1.78 g of fluorenylethylamine and 1.84 g of triethylamine is refluxed in 50 ml of ethanol under nitrogen for 20 hrs. Upon cooling, solid material crystallizes out. It is filtered and dried affording 2.75 g (95%) of N⁶ -fluorenylethyl adenosine having a melting point of 120°-123° C.

Anals. Calcd. for C₂₅ H₂₅ N₅ O₄ 0.25EtOH: C=65,00; H=5.67; N=14.87. Found: C=64.76; H=5.79; N=15.02.

EXAMPLE 4 N⁶ -[Xanthene-9-methylamino]adenosine

A mixture of 2.44 g of 6-chloropurine riboside, 2.0 g of 9-methylaminoxanthene, and 1.07 g of triethylamine are refluxed in 60 ml of ethanol, under nitrogen, for 22 hours. The solvent is evaporated and the residue is treated with 150 ml of cold water. The solid material obtained is recrystalyzed from chloroform-hexane, affording 1.45 g (37%) of N⁶ -[xanthene-9-methylamino]adenosine having a melting point of 93°-95° C.

Anals. Calcd. for C₂₄ H₂₃ N₅ O₅ : C=62.47; H=5.02; N=15.18. Found: C=62.18; H=5.30; N=14.40. 

We claim:
 1. A method for treating hypertension in a mammal suffering therefrom, which comprises administering to such mammal an antihypertensive effective amount of a compound of the formula ##STR6## wherein R⁶ a is hydrogen or lower alkyl; R⁶ b is hydrogen, hydroxy, lower alkyl, lower alkanoyloyx- or benzoyloxy; R⁶ c and R⁶ d are each independently hydrogen or one or more substituents selected from halogen, hydroxy, lower alkoxy, lower alkanoyloxy, benzoyloxy, lower S(O)n--alkyl in which n is zero, one, or two, sulfonamide, trifluoromethyl, lower alkyl, lower mono- or dialkylamino, nitro or sulfhydryl; X is a valence bond or a straight or branched alkylene of one to eight carbon atoms; Y is a valence bond, oxygen, sulfur, NR in which R is hydrogen, lower alkyl, lower alkanoyl or benzoyl, --(CH₂)n-- in which n is one or two or --CH═CH--; R² is hydrogen, halogen, NR^(i) R^(ii), OR^(i) or SR^(i) in which R^(i) and R^(ii) are each independently hydrogen, lower alkyl or phenyl, lower alkyl; R² ', R³ ', and R⁵ ' are each independently hydrogen, lower alkanoyl, benzoyl, or benzoyl subsituted by lower alkyl, lower alkoxy, halogen or trifluoromethyl, or R² ' and R³ ' may be bonded together to form a lower alkylidene group, on a pharmaceutically acceptable acid from salt thereof in unit dosage form.
 2. A method as claimed in claim 1, wherein R₆ ^(a) and R₆ ^(b) are hydrogen.
 3. A method as claimed in claim 1, wherein R₆ ^(a), R₆ ^(b), R₆ ^(c), and R₆ ^(d) are hydrogen.
 4. A method as claimed in claim 3, where X is a valence bond, methylene or ethylene and Y is a valence bond or oxygen.
 5. A method as claimed in claim 4, wherein R₂ is hydrogen.
 6. A method as claimed in claim 5, wherein R² ', R³ ', and R⁵ ' are hydrogen.
 7. A method as claimed in claim 6, and being N⁶ -fluorenyladenosine.
 8. A method as claimed in claim 6, and being N⁶ -fluorenylmethyladenosine.
 9. A method as claimed in claim 6, and being H⁶ -fluorenylethyladenosine.
 10. A method as claimed in claim 6, and being [N⁶ -(xanthene-9-methyl-amino)adenosine]N⁶ -(9-methylaminoxanthenyl)adenosine. 